1. Field of the Invention
The present invention relates to a bumper beam structure which functions as a frame portion of a bumper of a vehicle.
Priority is claimed on Japanese Patent Application No. 2004-372917, filed Dec. 24, 2004, the content of which is incorporated herein by reference.
2. Description of the Related Art
In a bumper of a vehicle (i.e., a vehicle bumper), a bumper beam extending in a width direction of the vehicle is attached to ends of a pair of side frames, and a bumper face made of resin is attached to the front side of the bumper beam.
Recently, a structure in consideration of a low-speed crash against a support pole or the like (called a “pole crash”, hereinbelow) is sometimes employed for the vehicle bumper. Such a vehicle bumper has a specific bumper beam structure for flexibly absorbing a load in a crash (see, for example, Japanese Unexamined Patent Application, First Publication No. H6-286536).
In the disclosed bumper beam structure, a bumper beam main body is integrally formed by extrusion molding using an aluminium material, and a center gusset formed as a separated body is joined to substantially the center of the bumper beam main body in the length direction thereof. The center gusset is attached and fastened to the front face of the bumper beam main body (i.e., the face to which the bumper face is attached), thereby producing a closed-section form at the front side of the bumper beam main body.
In the above bumper beam structure, when a pole crash occurs, the center gusset positioned at substantially the center of the bumper beam main body receives a load from a support pole or the like and is easily crushed. A further load input makes the bumper beam main body bend, and finally a section of the deformed bumper beam main body is crushed.
In the above conventional bumper beam structure, in order to reliably make the center gusset crush first when a pole crash occurs, it is necessary to improve the geometrical moment of inertia of a support portion (in the bumper beam main body) for the center gusset. However, in the conventional bumper beam structure, the bumper beam main body is a metal body formed by extrusion molding. Therefore, when the geometrical moment of inertia of the support for the center gusset is improved by increasing the thickness thereof, the thickness of the whole bumper beam main body should be increased, so that the weight of the vehicle is increased.
In addition, such an increase in the thickness of the whole bumper beam main body causes an increase in a load for crushing a section of a side edge of the bumper beam main body. Therefore, it is difficult to perform tuning for delaying buckling of a vehicle's side frame in comparison with the crushing of a section of the bumper beam main body when a high-speed offset crash occurs.